mirror of https://github.com/SixLabors/ImageSharp
James Jackson-South
4 years ago
committed by
GitHub
GitHub
12 changed files with 345 additions and 39 deletions
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// Copyright (c) Six Labors.
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// Licensed under the Apache License, Version 2.0.
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using System; |
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using System.Buffers; |
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using SixLabors.ImageSharp.Advanced; |
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using SixLabors.ImageSharp.Formats.Webp.Lossless; |
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using SixLabors.ImageSharp.Memory; |
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using SixLabors.ImageSharp.PixelFormats; |
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namespace SixLabors.ImageSharp.Formats.Webp |
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{ |
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/// <summary>
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/// Methods for encoding the alpha data of a VP8 image.
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/// </summary>
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internal class AlphaEncoder : IDisposable |
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{ |
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private IMemoryOwner<byte> alphaData; |
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/// <summary>
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/// Encodes the alpha channel data.
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/// Data is either compressed as lossless webp image or uncompressed.
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/// </summary>
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/// <typeparam name="TPixel">The pixel format.</typeparam>
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/// <param name="image">The <see cref="ImageFrame{TPixel}"/> to encode from.</param>
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/// <param name="configuration">The global configuration.</param>
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/// <param name="memoryAllocator">The memory manager.</param>
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/// <param name="compress">Indicates, if the data should be compressed with the lossless webp compression.</param>
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/// <param name="size">The size in bytes of the alpha data.</param>
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/// <returns>The encoded alpha data.</returns>
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public IMemoryOwner<byte> EncodeAlpha<TPixel>(Image<TPixel> image, Configuration configuration, MemoryAllocator memoryAllocator, bool compress, out int size) |
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where TPixel : unmanaged, IPixel<TPixel> |
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{ |
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int width = image.Width; |
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int height = image.Height; |
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this.alphaData = ExtractAlphaChannel(image, configuration, memoryAllocator); |
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if (compress) |
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{ |
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WebpEncodingMethod effort = WebpEncodingMethod.Default; |
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int quality = 8 * (int)effort; |
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using var lossLessEncoder = new Vp8LEncoder( |
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memoryAllocator, |
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configuration, |
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width, |
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height, |
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quality, |
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effort, |
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WebpTransparentColorMode.Preserve, |
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false, |
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0); |
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// The transparency information will be stored in the green channel of the ARGB quadruplet.
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// The green channel is allowed extra transformation steps in the specification -- unlike the other channels,
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// that can improve compression.
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using Image<Rgba32> alphaAsImage = DispatchAlphaToGreen(image, this.alphaData.GetSpan()); |
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size = lossLessEncoder.EncodeAlphaImageData(alphaAsImage, this.alphaData); |
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return this.alphaData; |
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} |
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size = width * height; |
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return this.alphaData; |
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} |
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/// <summary>
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/// Store the transparency in the green channel.
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/// </summary>
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/// <typeparam name="TPixel">The pixel format.</typeparam>
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/// <param name="image">The <see cref="ImageFrame{TPixel}"/> to encode from.</param>
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/// <param name="alphaData">A byte sequence of length width * height, containing all the 8-bit transparency values in scan order.</param>
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/// <returns>The transparency image.</returns>
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private static Image<Rgba32> DispatchAlphaToGreen<TPixel>(Image<TPixel> image, Span<byte> alphaData) |
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where TPixel : unmanaged, IPixel<TPixel> |
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{ |
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int width = image.Width; |
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int height = image.Height; |
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var alphaAsImage = new Image<Rgba32>(width, height); |
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for (int y = 0; y < height; y++) |
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{ |
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Memory<Rgba32> rowBuffer = alphaAsImage.DangerousGetPixelRowMemory(y); |
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Span<Rgba32> pixelRow = rowBuffer.Span; |
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Span<byte> alphaRow = alphaData.Slice(y * width, width); |
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for (int x = 0; x < width; x++) |
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{ |
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// Leave A/R/B channels zero'd.
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pixelRow[x] = new Rgba32(0, alphaRow[x], 0, 0); |
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} |
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} |
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return alphaAsImage; |
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} |
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/// <summary>
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/// Extract the alpha data of the image.
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/// </summary>
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/// <typeparam name="TPixel">The pixel format.</typeparam>
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/// <param name="image">The <see cref="ImageFrame{TPixel}"/> to encode from.</param>
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/// <param name="configuration">The global configuration.</param>
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/// <param name="memoryAllocator">The memory manager.</param>
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/// <returns>A byte sequence of length width * height, containing all the 8-bit transparency values in scan order.</returns>
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private static IMemoryOwner<byte> ExtractAlphaChannel<TPixel>(Image<TPixel> image, Configuration configuration, MemoryAllocator memoryAllocator) |
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where TPixel : unmanaged, IPixel<TPixel> |
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{ |
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Buffer2D<TPixel> imageBuffer = image.Frames.RootFrame.PixelBuffer; |
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int height = image.Height; |
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int width = image.Width; |
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IMemoryOwner<byte> alphaDataBuffer = memoryAllocator.Allocate<byte>(width * height); |
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Span<byte> alphaData = alphaDataBuffer.GetSpan(); |
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using IMemoryOwner<Rgba32> rowBuffer = memoryAllocator.Allocate<Rgba32>(width); |
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Span<Rgba32> rgbaRow = rowBuffer.GetSpan(); |
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for (int y = 0; y < height; y++) |
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{ |
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Span<TPixel> rowSpan = imageBuffer.DangerousGetRowSpan(y); |
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PixelOperations<TPixel>.Instance.ToRgba32(configuration, rowSpan, rgbaRow); |
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int offset = y * width; |
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for (int x = 0; x < width; x++) |
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{ |
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alphaData[offset + x] = rgbaRow[x].A; |
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} |
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} |
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return alphaDataBuffer; |
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} |
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/// <inheritdoc/>
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public void Dispose() => this.alphaData?.Dispose(); |
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} |
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} |
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@ -0,0 +1,3 @@ |
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version https://git-lfs.github.com/spec/v1 |
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oid sha256:843bea4db378f52935e2f19f60d289df8ebe20ddde3977c63225f1d58a10bd62 |
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size 48119 |
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